This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Pipes, vessels, and other enclosures are often insulated for any number of reasons. For example, to lower heat loss in hot systems, heat gain in cold systems, protect personnel, and increase fire resistance. However, the use of insulation hides the surface of the enclosure from easy inspection. Accordingly, corrosion under the insulation (CUI) can form without easy detection.
CUI has challenged the oil and gas industry for years by causing unscheduled downtime from pipe and vessel failures, safety and environmental concerns, and downtime for inspections. CUI generally occurs as a result of water coming in contact with the metal of an enclosure, such as a pipe, vessel, or other metal structure, in an oxygen environment under an insulation layer, which results in corrosion. Water can make its way into the annular space between pipe and insulation through several methods, including rainfall and firewater discharge and in some cases may be present in the insulating material itself. In carbon steels, CUI can manifest itself as wall thickness loss or pitting. In stainless steels, the most common form of corrosion from CUI is chloride stress corrosion cracking caused by chloride deposits. The chlorides are deposited on the pipe after water with chloride salts evaporates from the outer surface of a pipe, vessel, or other enclosure. A number of techniques are used to prevent CUI, such as waterproofing the system, using corrosion inhibitors, or applying protective coating systems. Each of these methods have advantages and disadvantages, but they do not offer a means of detecting CUI.
Current methods for detecting CUI can be costly and time consuming. For example, CUI is most commonly detected by removing the insulation over an area of an enclosure or by cutting and removing small areas to allow for visual inspection or ultrasonic testing. However, cutting the insulation can, itself, provide a pathway for water into the annular space between insulation and pipe. CUI can also be localized, causing visual inspections to miss affected areas. Other detection methods include radiography, x-ray, electromagnetic, ultrasound, neutron backscatter, and eddy current devices. These may involve scanning long sections of pipe with complicated sensing devices calibrated to particular pipe thicknesses, material, etc.
Previous efforts have focused on either keeping the pipe dry or monitoring the humidity in the environment to detect moisture that may lead to CUI. For example, U.S. Patent Application Publication No. 2013/0344762 is directed to an insulation composition that includes a multi-layer structure. A first layer is a hydrophobic, moisture permeable layer composed of a woven, non-woven, or knit fibrous material. A second layer is a hydrophilic wicking layer, and a third layer is an insulation material layer. A method is provided to remove water from an insulated metal transport conduit comprising a metal transport conduit and an insulation composition. The insulation composition includes a layer of a high void material, through which a stream of gas is flowed from a first point. The stream of gas picks up water from the high void material and discharges it at a second point. A method is provided to detect and locate liquid water in an insulation composition positioned around a metal transport conduit by measuring the local electric conductivity in a wicking material.
U.S. Patent Application Publication No. 2013/0063602 is directed to an apparatus for monitoring humidity exposure of system components. The apparatus includes sensor modules for collecting environmental data and a monitoring module with a humidity indicator. An electrical monitoring component sealed from the environment reads a physical change in the humidity indicator to determine the humidity of the environment. A computer may transmit the humidity data and sensor readings, wirelessly or otherwise, to a central monitoring station for processing and storage. The humidity indicator may be disposed within an enclosure to determine the humidity within that enclosure. The humidity indicator may also be a desiccant that changes color cased on the humidity, and the electrical monitoring component may be a camera configured to take video data of the desiccant.
Active systems to detect or remove moisture may be complex or vulnerable to failures. Research into the development of more simple systems is progressing.